1. Field of the Invention
The present invention relates generally to face gears and, more particularly, to methods for forging face gears and the resulting forged face gears.
2. Description of Related Art
Face gears are widely used in low power applications, but often are not strong enough for use in high power applications. Present manufacturing methods for cutting face gear teeth incorporate hobs or shapers. FIG. 1 illustrates a face gear 12 having face gear teeth 14 and face gear gaps 16. A shaper gear 18 comprises shaper gear teeth 21 and shaper gear gaps 23. The shaper gear 18 rotates about a shaper gear axis of rotation Z.sub.s with a shaper gear rotational velocity .omega..sub.s. The face gear 12 rotates about a face gear axis of rotation Z.sub.g with a face gear rotational velocity .omega..sub.g. As the shaper gear 18 rolls over the face gear 12, the shaper gear teeth 21 and the shaper gear gaps 23 form the face gear gaps 16 and the face gear teeth 14, respectively. The shaper gear 18 further comprises a shaper gear y-axis Y.sub.s and a shaper gear x-axis X.sub.s. The face gear 12 comprises a face gear y-axis Y.sub.g and a face gear x-axis X.sub.g.
The face gear teeth 14 and the face gear gaps 16 accommodate a spur gear during regular operation, after the face gear 12 has been shaped by the shaper gear 18 and the shaper gear 18 removed. FIG. 2 illustrates a face-gear drive 35 comprising a face gear 12, and a spur gear 40. The spur gear 40 comprises a conventional involute gear and the face gear 12 is constructed to obey conjugate action with the spur gear 40. The axes of the face gear 12 and of the spur gear 40 intersect and are perpendicular to one another. Face-gear drives having non-intersecting and non-orthogonal axes exist, as well.
The conventional face gear teeth 14 and face gear gaps 16, after being formed by the shaper gear 18 of FIG. 1, are not sufficiently strong for high power applications. The face gear 12 may be case hardened to thereby increase the strength and wear characteristics of the face gear teeth 14 and face gear gaps 16. Case-hardening techniques, such as carburizing and nitriting heat-treat methods, induce distortions in the face gear teeth 14 and gaps 16 of the face gear 12. These distortions prevent smooth operation of the spur pinion on the face gear teeth 14 and, further, the shaper gear 18 is not appropriate for attenuating the distortions in the hardened face gear 12. Grinding processes have been used in the past for finishing gear tooth surfaces in gears other than face gears, when the gears have been heat treated to a high hardness level after being originally cut.
As an alternative to the shaper gear 18, a hob 25 as illustrated in FIG. 3 may be used for forming the face gear teeth 14 and face gear gaps. The hob 25 typically comprises an axis of rotation 27, and a plurality of hob teeth 30 and recessed areas 31 disposed along the perimeter of the hob 25. As the hob 25 is rotated about the axis of rotation 27 in the direction of the arrow A1, the hob teeth 30 cut into the face gear 12 to thereby form the face gear teeth 14 and face gear gaps 16. U.S. Pat. No. 2,304,588 to Miller discloses such a hob used for cutting teeth into a face gear.
An end view of the hob 25 contacting the face gear 12 is illustrated in FIG. 4. The hob 25 comprises a first hob tooth 32, a second hob tooth 34, and a third hob tooth 36. As the hob 25 rotates about the axis of rotation 27 (FIG. 3), the first hob tooth 32 contacts the first face gear tooth 38. Additionally, the second hob tooth 34 and the third hob tooth 36 contact the second face gear tooth 41. The first, second, and third hob teeth 32, 34, and 36 machine (or cut) the first and second face gear teeth 38 and 41. This machining process, however, is not suitable for use on a case-hardened face gear. Additionally, the hob teeth 30 are not properly shaped and, consequently, the face gear teeth 14 of the Miller apparatus are not correctly cut.
Although high-power applications would be desirable for face-gear drives, the conventional gear roughing processes of shaping and hobbing, for example, do not adequately rough the teeth of the face gear. An effective method of roughing the gear teeth of the face gear is required to properly prepare the gear teeth for finishing. One problem associated with prior-art shaping and hobbing techniques is that, being metal cutting processes, these techniques leave gear teeth with interrupted material grain flow. The interrupted material grain flow weakens the strength of the gear teeth. Additionally, relatively high tooling costs are associated with the relatively complex tools required for shaping and hobbing techniques. Shaping and hobbing techniques inherently waste a portion of the metal of the face gear as the face gear is shaped or hobbed. Conservation of the materials comprising the face gear becomes increasingly important as new, expensive materials are considered for aerospace gears, for example.
The prior art has manufactured spur gears, helicle gears, and spiral bevel gears using forging operations. Near-net forging of these particular gears can produce gears which meet sufficient accuracy requirements for subsequent, relatively efficient finishing operations. The forged gears can offer gear teeth having increased strength due to better oriented grain-flow patterns. Additionally, forging of the gears can reduce the amount of wasted metal and can potentially lower tooling and operating costs. Net or near-net forging procedures, however, have not been developed for manufacturing face gears.